1. Field of the Invention
The present invention pertains generally to the field of cementing equipment, and more particularly to a cement head apparatus used for subsea cementing operations.
2. Background
Traditionally, in the oil field industry rubber darts and/or rubber balls are used for a down hole cementing operation and are held in a cementing head up and out of the cement slurry flow path. The rubber darts and/or balls are released at the appropriate time to join into the cement flow moving down hole. FIG. 1 depicts one such traditional approach. This prior art's approach requires that the cement slurry flow into the cement head from a cement inlet on the sides. This approach works for cement heads which use a manifold system, but is saddled with several disadvantages, particularly with respect to subsea applications. First, the prior art cement heads do not have any lifting capacity or tensile strength. Second, they do not have a rotational capacity to swivel the cement flow because the slurry is flowing into them from the sides.
In subsea well drilling applications using off-shore drilling platforms or specialized drilling boats, the pipe lifting system must have the ability to simultaneously lift 750 metric tons (1,653,450 lbs.) of pipe, and have the ability to rotate at 50 rpm to assure sufficient swivel of the cement flowing into the pipes, and further have the flow capacity of up to 60 barrels per minute of cement flow at the speeds of up to 50 feet per second. Accordingly, the cement head must have the capacity to endure combined lift to pressure ratios of up to 500 metric tons at 10,000 psi working pressure. Therefore, there is a strong desire for a cement head in which cement flows into the cement head from the top and further has a high tensile strength and a capacity for swivel.